This invention relates to a magnetic device including a magnetoresistive element such as a magnetic head for recording an information signal on and/or reading/reproducing an information signal from a magnetic medium, a method for manufacturing such a head and a magnetic recording apparatus using such a head.
This application is based on Japanese Patent Application No. Hei 11-1153051, the contents of which are incorporated herein by reference.
Various documents disclose a transducer for the magnetic data reading called a magnetoresistive sensor (hereinafter referred to as xe2x80x9cMR sensorxe2x80x9d) or head, and it has been known that such a sensor can read data from a magnetized surface at a high linear density. The MR sensor detects a magnetic field signal through a change in resistance which is sensed by a read element as a function of the strength and direction of the magnetic flux. This type of conventional MR sensor operates based on the anisotropic magnetoresistive effect (hereinafter referred to as xe2x80x9cAMR effectxe2x80x9d) in which one component of the resistance of the read element changes in proportion to the square of the cosine of the angle between the direction of magnetization and the direction of the sense current flowing through the element. The AMR effect is described in detail by D. A. Thompson et al. in the article xe2x80x9cMemory, Storage and Related Applicationsxe2x80x9d, IEEE Trans. on Mag. MAG-11, page 1039 (1975). In magnetic heads utilizing the AMR effect, a longitudinal bias is often applied to suppress Barkhausen noise wherein an antiferromagnetic material such as FeMn, NiMn and nickel oxide is used as the longitudinal biasing material.
Recently, some documents have described a more remarkable magnetoresistive effect in which the change in resistance in a laminated magnetic sensor is caused by a spin-dependent transmission of conduction electrons between magnetic layers through a nonmagnetic layer and the accompanying spin-dependent scattering at the interface of the layers. This magnetoresistive effect is called by various names such as xe2x80x9cgiant magnetoresistive effectxe2x80x9d and xe2x80x9cspin-valve effectxe2x80x9d. This type of magnetoresistive sensor is made of appropriate materials and has an improved sensitivity and a larger resistance change as compared to those observed in a sensor utilizing the AMR effect. In an MR sensor of this type, the resistance in a plane between a pair of ferromagnetic layers separated by a nonmagnetic layer changes in proportion to the cosine of the angles between the directions of magnetization of the two layers.
Japanese Unexamined Patent Application, First Publication No. Hei. 2-61572 which claims a priority of June 1988 discloses a laminated magnetic structure which can provide a large MR change caused by an antiparallel alignment of magnetizations in the magnetic layers. The specification of this publication refers to ferromagnetic transition metals and alloys as materials which can be used in the laminated structure. It also discloses a structure in which a pinning layer is added to at least one of the two ferromagnetic layers separated by an intermediate layer, and the fact that FeMn is suitable for the pinning layer.
Japanese Unexamined Patent Application, First Publication No. Hei. 4-103014 filed on Aug. 22, 1990, describes a ferromagnetic tunnel junction film which takes the form of a multilayer film having an intermediate layer inserted between ferromagnetic layers, wherein a biasing magnetic field from an antiferromagnetic material is applied to at least one of the ferromagnetic layers.
Japanese Unexamined Patent Application, First Publication No. Hei 10-162327 which claims a priority of Nov. 27, 1996 describes about an example of reproducing heads with a ferromagnetic tunnel junction film which has such a structure that a layer (longitudinal biasing layer) for controlling magnetic domains in the free layer does not contact the free layer, wherein a film of a material other than the metallic materials constituting the ferromagnetic tunnel junction film is formed.
There has been proposed a shield type magnetoresistive effect element utilizing a ferromagnetic tunnel junction film which has such a structure that the longitudinal biasing layer is prevented from directly contacting the ferromagnetic tunnel junction film by means of an insulating material such as alumina (see Japanese Unexamined Patent Application, First Publication No. Hei 10-162327). This is to solve the problem that, although in the case of a shield type element with a ferromagnetic tunnel junction a sense current should flow through the tunnel junction portion perpendicularly thereto, with a structure similar to that of the conventional shield type element utilizing a spin valve a sense current bypasses the barrier layer and flows through the longitudinal biasing portion which is located near the barrier layer and has lower resistance value than that of the barrier layer, as a result of which the sense current does not contribute to the detection of the resistance change. However, since this structure is attained by means of a process of further forming a film of alumina upon end portions of the ferromagnetic tunnel junction film formed by patterning in advance, during the patterning process of the ferromagnetic tunnel junction film, metal is scattered when patterning those of the layers constituting the ferromagnetic tunnel junction film which are disposed below the barrier layer, and the scattered metal is redeposited on side walls of those layers including the barrier layers which have already been patterned. Consequently, the sense current bypasses the barrier layer and flows through the redeposited layer in the finished element, causing the MR ratio to be significantly reduced.
It is therefore an object of the present invention to provide a magnetoresistive effect element which is easy to manufacture and in which the sense current is prevented from bypassing the barrier layer.
It is another object of the invention to provide a method for manufacturing such a magnetoresistive effect element.
It is a further object of the invention to provide an apparatus which uses such a magnetoresistive effect element.
In the first aspect of the present invention, a magnetoresistive effect element comprising: a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer and a pinned layer formed on the barrier layer or an arrangement of a pinned layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, wherein pattern of the ferromagnetic tunnel junction film comprises an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film.
In the second aspect of the invention, a magnetoresistive effect element comprising: a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, wherein a pattern of the ferromagnetic tunnel junction film comprises an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film.
In the third aspect of the invention, a magnetoresistive effect element comprising: a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of an underlayer, a free layer formed on the underlayer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of an underlayer, a pinning layer formed on the last-mentioned underlayer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, wherein a pattern of the ferromagnetic tunnel junction film comprises an oxide or a nitride of a metallic material constituting the underlayer.
In the fourth aspect of the invention, a magnetoresistive effect element comprising: a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer, a pinning layer formed on the pinned layer and a protective layer formed on the pinning layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer, a free layer formed on the last-mentioned barrier layer and a protective layer formed on the last-mentioned free layer, wherein a pattern of the ferromagnetic tunnel junction film comprises an oxide or a nitride of a metallic material constituting the protective layer.
In the fifth aspect of the invention, a magnetoresistive effect element comprising: a substrate; a lower shield layer formed on the substrate; a lower electrode layer, at least a portion of which is formed on the lower shield layer or combined with the lower shield layer; a longitudinal biasing layer formed on the lower electrode layer and patterned so as to have a width which is smaller than that of the lower shield layer when viewed from an air-bearing surface of the head; a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, at least a part of the free layer being disposed above the longitudinal biasing layer and adjoining the longitudinal biasing layer directly or with an underlayer interposed therebetween; an insulating layer formed at least on a part of the free layer and the longitudinal biasing layer; an upper electrode layer formed above the pinning layer and adjoining, at least at a part thereof, the pinning layer directly or with a protective layer interposed therebetween; and an upper shield layer, at least a part of which is formed on or combined with the upper electrode layer; wherein an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film is present at an end portion or a peripheral portion of a pattern of the ferromagnetic tunnel junction film.
In the sixth aspect of the invention, a magnetoresistive effect element comprising: a substrate; a lower shield layer formed on the substrate; a lower electrode layer, at least a portion of which is formed on or combined with the lower shield layer; a longitudinal biasing layer formed on the lower electrode layer and patterned so as to have a width which is smaller than that of the lower shield layer when viewed from an air-bearing surface of the head; a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, at least a part of the free layer being disposed below the longitudinal biasing layer and adjoining the longitudinal biasing layer directly or with an underlayer interposed therebetween; an insulating layer formed on at least a part of the free layer and the longitudinal biasing layer; an upper electrode layer formed on the pinning layer and adjoining, at least at a portion thereof, the pinning layer directly or with a protective layer interposed therebetween; and an upper shield layer, at least a part of which is formed on or combined with the upper electrode layer; wherein an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film is present at an end portion or a peripheral portion of a pattern of the ferromagnetic tunnel junction film.
In the seventh aspect of the invention, a magnetoresistive effect element comprising: a substrate; a lower shield layer formed on the substrate; a lower electrode layer, at least a portion of which is formed on or combined with the lower shield layer; a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, the film being formed on the lower electrode layer, the free layer having a width equal to or less than that of the lower electrode layer when viewed from an air-bearing surface of the element; a longitudinal biasing film comprising a film formed by laminating an insulating layer, at least a portion of which adjoins the free layer, and a longitudinal biasing layer formed on the insulating layer, or an insulating material; an upper electrode layer disposed above the free layer and adjoining, at least at a portion thereof, the free layer directly or with a protective layer interposed therebetween; and an upper shield layer, at least a part of which is formed on or combined with the upper electrode layer; wherein an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film is present at an end portion or a peripheral portion of a pattern of the ferromagnetic tunnel junction film.
In the eighth aspect of the invention, a magnetoresistive effect element comprising: a substrate; a lower shield layer formed on the substrate; a lower electrode layer, at least a portion of which is formed on or combined with the lower shield layer; a ferromagnetic tunnel junction film which comprises, for forming a basic structure thereof, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer, the film being formed on the lower electrode layer, the free layer having a width equal to or less than that of the lower electrode layer when viewed from an air-bearing surface of the element; an insulating layer adjoining at a part thereof the free layer; a longitudinal biasing layer disposed above the free layer and adjoining, at least at a part thereof, the free layer directly or with an interface control layer interposed therebetween; an upper electrode layer disposed above the longitudinal biasing layer and adjoining, at least at a portion thereof, the longitudinal biasing layer; and an upper shield layer, at least a part of which is formed on or combined with the upper electrode layer; wherein an oxide or a nitride of a metallic material constituting the ferromagnetic tunnel junction film is present at an end portion or a peripheral portion of a pattern of the ferromagnetic tunnel junction film.
In the ninth aspect of the invention, a method for manufacturing a magnetoresistive effect element which utilizes as its magnetoresistive effect element a ferromagnetic tunnel junction film comprising the steps of: forming a basic structure of the ferromagnetic tunnel junction film, an arrangement of a free layer, a barrier layer formed on the free layer and a pinned layer formed on the barrier layer or an arrangement of a pinned layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer; and after patterning the ferromagnetic tunnel junction film, oxidizing or nitriding an end portion of the patterned ferromagnetic tunnel junction film.
In the tenth aspect of the invention, a method for manufacturing a magnetoresistive effect element which utilizes as its magnetoresistive effect element a ferromagnetic tunnel junction film comprising the steps of: forming a basic structure of the ferromagnetic tunnel junction film, an arrangement of a free layer, a barrier layer formed on the free layer, a pinned layer formed on the barrier layer and a pinning layer formed on the pinned layer or an arrangement of a pinning layer, a pinned layer formed on the last-mentioned pinning layer, a barrier layer formed on the last-mentioned pinned layer and a free layer formed on the last-mentioned barrier layer; when the ferromagnetic tunnel junction film is patterned, stopping patterning the film in the middle of the layers constituting the magnetoresistive effect element; and oxidizing or nitriding at least a surface of that region of the magnetoresistive element at which the patterning has been stopped in the middle.
In the eleventh aspect of the invention, a magnetoresistive conversion system comprising: a magnetoresistive sensor comprising a magnetoresistive effect element; a current generating circuit for generating a current to be passed through the magnetoresistive sensor; and a data reading circuit for detecting a change in resistivity of the magnetoresistive sensor as a function of a detected magnetic field.
In the twelfth aspect of the invention, a magnetic storage system comprising: a magnetic recording medium having a plurality of tracks for data recording; a magnetoresistive conversion system; a first actuator for moving the magnetoresistive conversion system to a selected track on the magnetic recording medium; and a second actuator for driving the magnetic recording medium so as to rotate the magnetic recording medium.
In the case of the above-described magnetoresistive effect elements, after the ferromagnetic tunnel junction film (hereinafter referred to as xe2x80x9cMTJ filmxe2x80x9d) is formed, a layer composed of an oxide or nitride of the metallic materials constituting the pinned and pinning layers can be formed by oxidizing or nitriding the sidewall portions of at least the pinned and pinning layers of the MTJ film. Thus, the magnetoresistive effect head according to the invention is quite easy to manufacture. Even when a redeposited layer of metal is formed on the sidewalls of the MTJ film thus patterned, it is possible to prevent a current from bypassing the barrier layer by oxidizing or nitriding the redeposited layer in the manufacturing process, since an oxide or a nitride formed thereby is an insulator and does not contribute to electric conduction. The yield can thus be improved.
Furthermore, it will be possible to obtain a magnetoresistive effect element which has little noise in its reproduction signal waveform, a higher S/N (Signal to Noise) ratio and a lower error rate. It is also possible to construct a high-performance magnetic recording (or recording/reproducing) apparatus by the employment of this magnetoresistive effect element.